This invention relates generally to photovoltaic (PV) power plants, and more particularly, to a system and method for coordinating the switching of distributed dc-dc converters associated with PV modules to yield highly efficient photovoltaic power plants.
PV plant architectures take several forms starting from the conventional central inverter system to a fully distributed system as shown in FIGS. 1-4, all of which can be considered to have multiple dc-dc power converters. FIG. 1, for example, illustrates a PV plant architecture 10 that employs a two-stage central inverter 12. FIG. 2 illustrates a PV plant architecture 20 that employs a string combiner distribution of dc-dc converters 22. FIG. 3 illustrates a PV plant architecture 30 that employs a string distribution of dc-dc converters 32. FIG. 4 illustrates a PV plant architecture 40 that employs a module level distribution of dc-dc converters 42.
Power converters are designed to have high efficiency over a range of its operating power. Maintaining power converter operation within this power range will result in significant energy savings. PV modules are not at their rated power for most of their operating time; therefore the dc-dc converter stage(s) associated with them are always operated at partial load and in many cases at light load. Well-designed power converters have a high efficiency that is relatively constant for a wide load range. Converter losses however, constitute a larger percentage of the input power as this power level becomes smaller and consequently, light load efficiency of these converters fall sharply.
Distributed PV plant architectures such as described above have benefits in increasing the energy yield of the plant. Distributed PV plant architectures provide, for example, more operational flexibility due to the availability of multiple dc-dc or dc-ac converters that can be controlled to operate simultaneously and share the generated power or switched in and out when needed. Although distributed PV plant architectures provide increased energy yield and operational flexibility, they still suffer from reduced power conversion efficiency at partial and/or light loading in PV power plants.
In view of the foregoing, there is a need for a method of operating distributed dc-dc converters associated with PV modules to yield highly efficient photovoltaic power plants that mitigate the effects of losses due to, for example, shading, soiling, mismatch, transient event, and the like.